Topics: The new Privacy Sandbox proposal for interest-based advertising

February 22, 2022

Chrome recently announced an updated Privacy Sandbox proposal called Topics to support interest-based advertising and help businesses connect with potential customers in a more private way. This new API replaces the Federated Learning of Cohorts (FLoC) proposal.

The Privacy Sandbox is a collaborative initiative to build new privacy-preserving technologies as an alternative to third-party cookies. The goal is to improve user privacy while preserving the vitality of the open web by supporting key marketing use cases for online businesses. Chrome has incorporated feedback from the industry to improve upon the initial FLoC proposal, and we found that we can make interest-based advertising more private with our new proposal, Topics.

With Topics API, a user’s browser determines a handful of topics such as “Beauty & Fitness” or “Running & Walking” that represent their top interests for the previous week based on their browsing activity. When a user visits a participating site, the API will share up to three topics—one from each of the past three weeks—with websites and their advertising partners who can use it as one of many potential signals for interest-based advertising. So if you’re promoting gym memberships or sports gear and you want to reach people interested in fitness, you can do so in a way that’s relevant and private.

Here are some ways that Topics will be more private: 

  • Reduces the risk of fingerprinting
    Launching a limited set of topics (350 in the first proposal) helps reduce the chance that individuals could be identified based on their unique topics of interest. In addition, the same user may have distinct topics assigned to them across different sites, and a small amount of noise will be added in the process, making it more difficult to reveal their identity.
  • Provides more human-understandable transparency
    Past feedback led us to explore new ways of making interest-based advertising in the Privacy Sandbox even more transparent and meaningful to users. On Chrome, users will be able to clearly recognize the topics they are associated with, such as “Pop Music” or “Tourist destinations”.
  • Continues to avoid sensitive categories
    The set of possible topics will be public and manually curated, to avoid inadvertently introducing sensitive ones. This list will be developed and maintained in collaboration with the internet ecosystem and will be shared externally so that users and the community can provide feedback.

In the current version of this proposal, Topics will be selected locally on people’s devices without involving any external servers. And to limit the amount of data associated with an individual at any given time, topics will only be stored for three weeks, after which they will be deleted. Chrome will make user controls available from the start, so users can see the topics generated based on their browsing history, remove them, or opt out of the Privacy Sandbox APIs entirely. 

The Privacy Sandbox is continuously evolving. As Topics API for the web becomes available, the ecosystem is encouraged to provide feedback to help inform potential improvements and next steps. And we are excited to see that similar proposals are being considered for Android

We invite you to review the proposal and engage with the open questions—such as what Topics should be included—and to stay up to date with the Privacy Sandbox roadmap.

Posted by Vinay Goel, Product Director, Chrome Privacy Sandbox

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